P. gingivalis activates the NADPH/PAD4 axis to drive macrophage extracellular trap formation and alveolar bone loss in periodontitis.

BACKGROUND: Macrophage extracellular traps (METs) exert dual roles in inflammatory diseases, yet their formation and regulation in periodontitis remain unclear. In particular, whether and how Porphyromonas gingivalis (P. gingivalis) triggers MET formation, and the underlying signaling pathways, have yet to be elucidated. METHODS: Experimental periodontitis was established in mice by ligation and local P. gingivalis administration, and assessed for bone resorption, inflammatory infiltration, and MET-like accumulation by micro-CT, H&E and immunofluorescence (IF). P. gingivalis -stimulated RAW264.7 cells were detected for MET-like formation and ROS. The role of METs was further probed in vivo using GSK484 or DNase I to block or clear METs. RESULTS: Mice with experimental periodontitis showed marked alveolar bone resorption, increased inflammatory infiltration, and enhanced MET accumulation in periodontal tissues. P. gingivalis induced MET release from RAW264.7 cells in a time-dependent manner, accompanied by ROS accumulation and increased histone H3 citrullination. DPI treatment reduced ROS levels, concomitantly inhibiting citrullinated histone H3 (Cit-H3) expression and MET-like formation. The GSK484 treatment did not affect the generation of ROS, but it did markedly suppress the production of Cit-H3 and the release of MET-like. In vivo, both GSK484 and DNase I treatment reduced MET-like accumulation, diminished inflammatory infiltration, suppressed osteoclast activation, and alleviated alveolar bone loss. CONCLUSIONS: P. gingivalis promotes the MET-like formation through the NADPH/PAD4 axis, thereby amplifying local inflammation and alveolar bone loss in periodontitis.